1. Field
The present embodiment relates to a manufacturing method of a thin film solar cell and a thin film solar cell module.
2. Description of the Related Art
A solar cell is a semiconductor device converting solar energy into electrical energy. The solar cell may be classified into a silicon type, a chemical compound type, and an organic material type according to its material.
A silicon system solar cell is classified into a single crystalline silicon solar cell, a polycrystalline silicon solar cell, and an amorphous silicon solar cell according to a phase of a semiconductor.
Further, the solar cell is classified into a bulk (substrate) type solar cell and a thin film type solar cell according to a thickness of a semiconductor. The thin film type solar cell has a semiconductor layer with a thickness of less than several tens of μm or several μm. A single crystalline silicon solar cell and a polycrystalline silicon solar cell of the silicon system solar cell belong to a bulk type. An amorphous silicon solar cell belongs to a thin film type.
Meanwhile, the chemical compound solar cell is classified into a bulk type consisting of Group III-V Gallium Arsenide (GaAs) and Group III-V Indium Phosphide (InP), and a thin-film type consisting of Group II-VI Cadmium Telluride (CdTe) and Group I-III-VI Copper Indium Diselenide (CIS; CuInSe2). The organic material solar cell is largely divided into an organic molecule type and organic/inorganic combination type. Besides these a dye-sensitized solar cell belongs to a thin-film type.
Among various types of solar cells, a bulk type silicon solar cell having high energy conversion efficiency has been widely used for ground power units.
However, in recent years, in the increasing demand for a bulk type silicon solar cell, the cost thereof has rapidly increased due to lack of materials. Consequently, so as to develop cost reduction and mass production technology of a solar cell for large-scale ground power units, there is a significant need for the development of a thin-film solar cell capable of significantly reducing silicon materials consumption.
In general, a wet cleaning process using deionized water has been widely used in mass production of a thin film solar cell.
In mass production of a current solar cell, a soda lime glass or a low iron tempered glass on which a transparent electrode is formed, is used as a substrate. In this case, the transparent electrode is made of a low iron tempered glass, an indium tin oxide (ITO), or a tin oxide (SnO2).
Further, a lightweight flexible substrate of low cost such as polyimide, polyethylen terephthalate (PET), PEN, aluminum (Al) foil, or stainless steel can be used.
When a substrate is contaminated with an organic material, a transparent electrode is readily peeled off from the substrate during formation of the solar cell, and the organic substances are diffused into an absorber layer, thereby reducing photo-electric conversion efficiency of the solar cell.
In addition, particles occurring during a unit process can be conveyed to other substrates through a conveyor or a robot in an in-line mass production line. During formation of the solar cell, particles can form pin holes. When conductive particles remain in a laser-patterning line, they may block insulation between adjacent unit cells to reduce yield and efficiency of a solar cell module.
Accordingly, so as to simultaneously achieve high efficiency and high yield in a mass production line of the solar cell, there is a need for multi-stage cleaning including initial cleaning, patterned transparent electrode cleaning, and cleaning after edge exclusion.
In this case, in the initial cleaning, a pure water cleaner using alkali detergent for cleaning is widely used to remove organic substances and particles formed on a surface of the substrate.
Moreover, in the patterned transparent electrode, when patterning a transparent electrode formed on a substrate by a laser scriber, a pure water cleaner is widely used to perform cleaning for removing particles formed on a surface of the substrate during patterning.
Subsequent to the transparent electrode cleaning, a substantial formation process of the solar cell is performed.
After a semiconductor layer is formed on a transparent electrode formed on the substrate, the resultant object is patterned in a laser patterning process. A metal electrode formed on the semiconductor layer is patterned, thereby constructing an internally serial-interconnected solar cell. Upon patterning the metal electrode, because conductive particles are produced, a cleaning process can be instantly performed by a pure water cleaner.
Next, after edge exclusion, a solar cell module is manufactured through works such as formation of a bus bar and assembling a module.
In this case, upon assembling a solar cell module, since an aluminum (Al) frame can be inserted, edge insulation is achieved. For the edge insulation, prior to formation of the bus bar, an edge exclusion process is carried out. The edge exclusion process removes semiconductor and conductive thin films formed or edge regions of the substrate to a predetermined width. In general, because a plurality of particles are produced during the edge exclusion process, after edge exclusion, cleaning is performed using a pure water clearer.
Although conventional pure water cleaners used in a mass production line of a thin film solar cell efficiently perform cleaning and remove particles, they have following disadvantages in terms of maintenance and management.
In general, because the pure water cleaner is composed of a unit sufficiently flowing pure water or detergent mixing water on a surface, a roll brush unit, a pure water rinsing unit, and an air knife unit removing moisture, a length of equipment is long to increase a total area of a mass production line of a solar cell.
Furthermore, since maintenance costs are increased and a large amount of waste water is generated in the production of a large amount of pure water and to manage resistance greater than a predetermined value, processing costs are high, which leads to an increase in total running costs.